EP0378517B1 - Burner for the combustion of gaseous fuels and/or liquid fuels in the gaseous state - Google Patents

Abstract

A blower produces in the space (44) in front of the screen (41) an air pressure and thus an airflow through the opening (43) into the mixing chamber (23). At the same time, gas flows out of the annular gas outlet (49) to the periphery of the airflow and out of the outlet openings (25) into the centre of the airflow. After practically noiseless ignition by the electrodes (45) in the mixing chamber (23), a short and stable flame is produced at the end of the mixing head (11). With a relatively strong air supply, the air pressure at the gas outlet openings (25) throttles the central gas emission in favour of the peripheral gas emission from the gas outlet (49). This contributes to the stability of the flame. The annular space (19) serves for recirculation of hot combustion gases to the inlet (13). <IMAGE>

Description

The invention relates to a burner for the combustion of gaseous and liquid fuels in the gaseous state, with a mixing head which has an inlet at the back and an outlet at the front, a flame tube surrounding the mixing head at a distance, the space between the mixing head and the flame tube serving as a recirculation channel for hot fuel gases for the inlet of the mixing head, an orifice arranged at the inlet of the mixing head with a passage for the air supply and means for fuel supply.

EP-A-0 175 875 describes a burner which is suitable either for operation with gas or for operation with oil. For this purpose, the burner has a gas nozzle or an atomizer nozzle for oil. Through the corresponding nozzle, the gas is blown into the mixing tube or the oil is injected into the mixing tube, into which the air required for combustion is also blown. A flame then forms at the front end of the mixing tube. Some of the hot combustion gases are then recirculated to the inlet of the mixing tube due to the injector effect of the combustion air introduced and mixed there with the gas / air or the oil mist / air mixture. The disadvantage here is that the mixture emerging from the mixing tube at high speed in the axial direction forms an elongated flame. There is therefore a relatively large flame zone with high temperatures, which favors the formation of nitrogen oxides. Another disadvantage is the noisy start-up shock when the gas mixture is ignited.

EP-A-0 283 435 describes a burner for the combustion of liquid fuels in the gaseous state, which has a rotating gasifier which is arranged at a distance from an air screen. At the outlet of the carburetor there is a mixing head with a deflection section and side outlets. The carburetor is surrounded by an electric heater. A flame tube surrounds the carburetor and the heater at a distance, whereby a recirculation path for hot fuel gases is created by the space between the carburetor and flame tube. This burner can only be operated with heating oil.

EP-A-0 048 438 describes a burner which can be operated with both heating oil and gas. This burner also has an orifice arranged in front of the oil atomizer device with an orifice opening which is coaxial with the oil atomizer device, the orifice opening being the only passage for the combustion air. A mixing tube is arranged coaxially downstream. In order to be able to operate the burner either with oil or gas, a second orifice is provided downstream of the first orifice with a second orifice arranged coaxially to the orifice of the first orifice. The two panels form an annular chamber for the supply of a heating gas. The annular chamber has an annular gas outlet opening in the area of the diaphragm opening. This burner also has the disadvantage that the fuel / air mixture emerging at high speed from the mixing tube in the axial direction forms an elongated hot flame which favors the formation of nitrogen oxides. It should also be noted that a current flows in the mixing tube that has a core of air with a jacket of gas.

WO-A-86 06150 shows a gas burner in which an air inlet chamber, a mixer and a gas metering tube are arranged coaxially to one another. The mixer consists of a piece of pipe which is closed at its free end and which can be axially displaced by a control rod arranged inside the gas metering pipe. In this case, a piece of pipe that is telescopically displaceable on the gas metering tube exposes or closes gas outlet openings. At the same time, the displacement of the mixer caused by the control rod releases or closes air inlet openings in the cylindrical air inlet plate she. The same thing happens simultaneously with the flame bores at the free end of the mixer. This burner has no means for recirculating hot fuel gases and therefore forms relatively hot flames, which promote the formation of NOX. The burner is also not suitable for operation with liquid fuels.

For environmental reasons, low NOX levels are aimed at today. With full power and a residual oxygen level of 3 percent, a maximum of 20 ppm NOX should be detectable. The impact should be low and a maximum of about 0.2 mbar. For safety reasons, however, strict requirements must also be placed on blower gas burners. So the burner should not only go beyond the control range intended for normal operation of about 1: 2.5 work safely, but also during adjustment work no conditions with risk of explosion or poisoning may occur. So even with a large excess of air, i.e. when the exhaust gas measurement shows about 8.5 to 11.5 CO₂, practically no toxic carbon monoxide should be formed (only about 10 to 50 ppm). The flame should also remain stable, even if the excess air is so large that only about 6 percent CO₂ is measured in the exhaust gases.

It is an object of the present invention to provide a burner of the type mentioned at the outset, which meets high environmental protection and safety requirements. In particular, the burner should generate little nitrogen oxides.

According to the invention, this is achieved by a burner according to claim 1. This burner produces a short, strongly expanding flame with a relatively low flame temperature. Thanks to the low flame temperature, only little nitrogen oxides are formed, so that the measured values of pollutants are far below the permissible maximum values set by the environmental protection authorities.

A gas supply pipe is advantageously provided as a means for supplying fuel, which extends through the passage in the diaphragm into the mixing head and has at least one gas outlet opening in the region of the inlet of the mixing head. However, the gas feed pipe expediently has a plurality of radial gas outlet openings. The radial outflow of the gas inside the mixing head ensures thorough mixing with the supplied air. This in turn enables the formation of a quiet, low-noise flame, which ensures optimal combustion.

The mixing head advantageously consists of a pipe section which has outlet openings at the front on the periphery and through the deflection part is completed. This enables a relatively cheap production. When operating with liquid fuel, the pipe section also serves as a carburetor. Thanks to the recirculation of hot gases, the pipe section is heated to a great extent, which practically prevents coking. The high temperature of the pipe section also causes the liquid fuel to evaporate reliably when the burner is switched off, so that at this stage there are no impermissible emissions of unburned hydrocarbons. The mixing head can be easily replaced during service work. In order to facilitate such a replacement, the gas supply pipe can have a fastening pin for receiving the mixing head.

It has proven to be expedient to provide wings or fins at the outlet openings of the mixing head, which are formed, for example, by punching from the wall of the pipe section. The exit of the combustible mixture is controlled by these wings, which leads to the formation of a favorable flame shape. The wings are advantageously arranged radially. But it is also possible to arrange the wings at an angle to the radius so that the flame gets a twist. The wings protrude inwards. This creates turbulence that leads to a good mixing of air and fuel.

Another embodiment provides that the mixing head has a deflection part with a plurality of fingers arranged on the periphery, for example triangular in cross-section, over which fingers a piece of pipe is slipped, wherein a gap between two fingers forms an outlet opening. This version is very stable and also ensures a stable flame.

The passage for the air supply provided in the diaphragm advantageously has a diameter that is smaller than the inside diameter of the mixing head. This creates a favorable injector effect for the recirculation of hot fuel gases.

A particularly favorable embodiment of the invention provides for a gas inlet to be provided in the passage for the air supply. This enables high flame stability over a large power control range. This gas inlet is advantageously ring-shaped. The gas is thus distributed to this air flow over the entire periphery of the air flow. It should be noted that the air pressure in the area of the gas outlet openings of the gas supply pipe is greater with a high air supply than with a low air supply. Due to the increased pressure, the gas outlet from the gas openings of the gas supply pipe is throttled. This changes the relationship between the central gas supply and peripheral gas supply in favor of the latter. So more gas flows on the periphery of the air flow. This contributes to high flame stability. The flame is held securely even with a high output or with a large excess of air.

The ignition electrodes can extend through the passage into the mixing head. The ignition then takes place within the mixing head. This enables the burner to start softly and quietly because the explosion-like start-up shock is so strongly dampened by the mixing head that it is barely audible.

Thanks to the deflection of the flame to the outside, it is possible to keep the flame tube short. It only needs to extend to the end of the mixing head. This has the advantage that there are no obstacles to the expansion of the flame and the formation of nitrogen oxides is thereby kept to a minimum.

When liquid fuel is supplied, the rear part of the mixing head serves as an evaporator.

Fig. 1

einen Schnitt durch den vorderen Teil eines Ausführungsbeispiels eines Brenners,

Fig. 2

einen Schnitt durch eine andere Ausführungsform eines Mischkopfes zur Verwendung bei einem Brenner wie in Fig. 1, und

Fig. 3

eine Ansicht von links des Mischkopfes von Fig. 2.

An embodiment of the burner will now be described with reference to the drawing. It shows:

Fig. 1

3 shows a section through the front part of an exemplary embodiment of a burner,

Fig. 2

a section through another embodiment of a mixing head for use in a burner as in Fig. 1, and

Fig. 3

a view from the left of the mixing head of Fig. 2nd

The sectional drawing of FIG. 1 shows the front part of a burner which is designed as a so-called two-fuel burner, that is to say as a burner which is optionally operated with gas or oil. The burner has a fan for the air supply in a known manner. However, only the burner head is shown in the sectional drawing.

The burner has a mixing head 11 which has an inlet 13 at the rear and at the front, i.e. flame side, has an outlet 15. The flame tube 17 is arranged coaxially at a distance from the mixing head 11 and extends approximately as far forward as the mixing head 11. The annular space 19 between the mixing head 11 and the flame tube 17 serves as a recirculation channel for hot fuel gases. A gas supply pipe 21 extends coaxially to the mixing head 11 into the mixing space 23. The gas supply pipe 21 has at least one gas outlet opening 25 in the area of the inlet 13. In the exemplary embodiment shown, a plurality of radially arranged gas outlet openings 25 are provided, which are arranged in several rows distributed over the circumference of the gas supply pipe 21. The gas supply pipe 21 also serves to fasten the mixing head 11. For this purpose, a fastening pin 31 is provided at the end of the gas supply pipe 21, which fits into a bore 33. The mixing head 11 is detachably fastened with the screw 35.

The mixing head 11 of FIG. 1 consists of a pipe section 12 and a deflection part 29 which is firmly connected to the mixing head 11 is. The pipe section has outlet openings 37 at the front on the periphery. In the embodiment shown, wings 39 are provided in the outlet openings 37, which are formed, for example, by punching from the wall of the pipe section 12. These wings 39 protrude radially inwards into the mixing space 23. However, it is also possible to arrange the wings 39 at an angle to the respective radius which leads to the root of the wing 39.

The mixing head 211 of FIGS. 2 and 3 basically has the same task and function as the mixing head 11 of FIG. 1 and can be installed in its place in the burner of FIG. 1. The mixing head 211 can be made, for example, from two parts 212 and 214, which are then connected to one another, for example, by press fitting or welding or brazing. The part 212 has a plate 229, which serves to deflect the gas mixture and has a plurality of fingers 237 on the periphery, which extend parallel to the axis 238. In the example shown, these fingers 237 have a practically triangular cross section. The part 214, which is formed by a tube piece, is put over the fingers 237. There are therefore outlet openings 237 in the front section of the mixing head 211 at the periphery. A bore 233 is used for the detachable fastening of the mixing head 211 to the fastening pin 31 of the gas supply pipe 21 from FIG. 1, a screw 35 again being able to serve as fastening means. This design of the mixing head is extremely stable and ensures a very uniform mixing of air and gas and a correspondingly uniform flame formation.

The reference number 41 denotes an aperture which is sealed off from the space 44 by means of the seal 42. The diaphragm 41 has a centrally arranged passage 43, which serves for the air supply. The diameter of this passage 43 is smaller than the inside diameter of the mixing head 11. The diameter of the passage 43 is expediently forty to ninety percent, preferably sixty percent, of the inside diameter of the mixing head 11. The electrodes 45 and the oil line 47 also extend through the passage 43 The electrodes 45 extend into the mixing chamber 23.

It is possible to provide an annular gas outlet 49 at the passage 43. For this purpose, in the exemplary embodiment shown, a disk 51 is fastened on the diaphragm 41 in such a way that a cavity 53 is created. This cavity 53 is connected to a further gas line 55. The opening 57 of the disk 51 has practically the same diameter as the opening 43 of the diaphragm 41.

When the burner is in operation, the blower (not shown) or in another way in the space 44 in front of the orifice 41 generates a pressure which can be approximately 12 mb. An air flow therefore arises through the passage 43 into the mixing space 23. At the same time, gas flows out of the annular gas outlet 49 and the outlet openings 25. The gas / air mixture that is created is ignited by the electrodes 45. The ignition takes place practically noiselessly in the mixing chamber 23, whereupon a short flame arises at the end of the mixing head 11. Hot combustion gases are recirculated through space 19 to inlet 13. This recirculation takes place on the basis of the Venturi effect, which is brought about by the air flowing through the passage 43.

It should be noted that the deflection part 27 deflects the air / fuel mixture in the radial or tangential direction away from the mixing head 11. It depends on the position of the wings 39 whether the direction of movement is more radial or tangential.

The flame generated in this way is very stable and, thanks to the possible expansion to the outside, has a relatively low flame temperature, so that practically no nitrogen oxides are generated. As already mentioned in the introduction, the start-up push is also low. Furthermore, the flame is held securely even under unfavorable conditions when the burner is adjusted and an impermissible production of carbon monoxide is prevented.

Various other embodiments of the invention are possible. Thus, the annular gas outlet 49 can be used in combination with a nozzle 21 'for liquid fuel, which, as shown in dashed lines, extends to just in front of the orifice 41 in order to spray heating oil into the mixing chamber 23 when required, which then serves as a carburetor works. In this case, the carburetor can be attached to the disk 51 with feet 20. The energy required for gasification is supplied by the recirculation of hot fuel gases through the space 19. The heating necessary for the start can take place either by operation with gas or by heating the mixing head 11 with an electric heater.

Finally, it should be pointed out the important advantage that the burner according to the invention is largely independent of the geometry of the combustion chamber of the boiler. In other words, the flame shape is hardly influenced by the shape of the boiler. Since the flame expands radially and is short, a relatively short combustion chamber is sufficient. After a short distance from the mixing head 11, the flame rests securely on the flame tube 17 and thus forms a flame curtain which separates the combustion chamber of the boiler from the annular space 19, so that the pressure conditions in the combustion chamber have no noticeable influence on the recirculation.

Claims (13)

1. A burner for burning gaseous and liquid fuels in the gaseous state (dual-fuel burner), comprising a mixing head (11) which serves to produce a mixture of air and fuel and which has an inlet (13) at the rear and an outlet (15) at the front, a flame tube (17) surrounding the mixing head (11) in spaced relationship and extending approximately as far as the end of the mixing head, the space (19) between the mixing head (11) and the flame tube (17) serving as a recycling duct for hot combustion gases to the inlet (13) of the mixing head (11), a gas supply pipe (21) disposed coaxially of the mixing head, means for supplying liquid fuel, a restrictor (41) disposed at the inlet (13) of the mixing head (11) and having a central passage (43) for the air supply, the gas supply, and the supply of liquid fuel, a deflection part (29) disposed at the outlet (15) of the mixing head (11) for deflecting the mixture of air and fuel in the radial or tangential direction away from the mixing head (11).
2. A burner according to claim 1, characterised in that the gas supply pipe (21) extends through the passage (43) in the restrictor (41) into the mixing head (11) and has at least one gas outlet aperture (25) in the region of the inlet (13) of the mixing head (11).
3. A burner according to claim 2, characterised in that the gas supply pipe (21) has a number of radial gas outlet apertures (25).
4. A burner according to any one of claims 1 to 3, characterised in that the mixing head (11) consists of a tubular member (12), which at the front has outlet apertures (15) at the periphery and is closed by the deflection part (29).
5. A burner according to claim 3 or 4, characterised in that the gas supply pipe (21) has a fixing pin (31) to accommodate the mixing head (11).
6. A burner according to claim 4 or 5, characterised in that blades (39) are provided at the outlet apertures (15) of the mixing head (11) and are formed, for example, from the tubular member wall by stamping.
7. A burner according to claim 6, characterised in that the blades (39) are disposed radially.
8. A burner according to claim 7, characterised in that the blades (39) are disposed at an angle to the radius.
9. A burner according to any one of claims 6 to 8, characterised in that the blades (39) project inwardly.
10. A burner according to any one of claims 1 to 9, characterised in that the mixing head (211) has a deflection part (212) with a plurality of fingers (239) disposed at the periphery, the fingers, for example, being of triangular cross-section and having a tubular member (214) fitted thereover, each gap (237) between two fingers (239) forming an outlet aperture.
11. A burner according to any one of claims 2 to 10, characterised in that the passage (43) provided for the air supply in the restrictor (41) has a diameter smaller than the inside diameter of the mixing head.
12. A burner according to any one of claims 2 to 11, characterised in that a gas outlet (49), for example of annular shape, is provided at the passage (43) for the air supply.
13. A burner according to any one of claims 1 to 12, characterised in that ignition electrodes (45) extend through the passage (43) into the mixing head (11).

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